The operation of an electronic camera will be explained as an example of a conventional image sensing apparatus.
FIG. 7 is a timing chart showing image sensing operation of a conventional electronic camera.
When an image sensing/recording instruction is issued by pressing a switch (e.g., shutter button), the electronic camera drives the shutter to perform exposure, and after exposure of a proper period, reads an image signal from the image sensing element. The image signal from the image sensing element is converted into image data via an A/D converter, and the image data is stored in the internal memory of the electronic camera or the like. Image data in the memory (stored in the memory) is corrected (scratch correction). The image sensing element may include a defective pixel, and this processing compensates for the defective pixel.
Image data in the memory is read out again, and subjected to data processing and calculation such as integration in order to perform white balance processing. This is a known technique, and a detailed description thereof will be omitted. Image processing is done with a white balance coefficient obtained by calculation. Image data (to be referred to as recording image data hereinafter) which is compressed after conversion into YUV data is stored in the memory again. At the same time, the YUV data is resized small, also compressed, and stored in the memory.
Various photographing condition data are also added and stored in the memory. Processing for the photographed image data is completed, and these data are recorded in association with photographed image data on a recording medium detachable from the electronic camera. The compressed recording image data is decompressed again, resized to a size suitable for display on a display device, and then displayed, so as to allow confirming image data recorded on the recording medium immediately after photographing on the display device such as the liquid crystal display of the electronic camera.
Some electronic cameras comprise a sequential shooting function of sensing a plurality of successive images by pressing the shutter button once. In sequential shooting, the above operation of obtaining recording image data is repeated to obtain successive recording image data. When the white balance coefficient is commonly used for the second and subsequent images attained by sequential shooting, data processing and calculation for performing white balance processing are executed for only the first image data of sequential shooting. Also in sequential shooting, a photographed image can be confirmed on the display device or the like. Similarly, compressed photographed image data is decompressed again, resized to a size suitable for display on the display device, and displayed.
However, the above-described processing in the electronic camera takes a long time until one photographing processing ends. The next photographing cannot be quickly executed, and a desired shutter chance may be missed. Also in sequential shooting, the sequential shooting interval becomes long. Display of a photographed image on the display device in sequential shooting prolongs the time interval after which the next photographing becomes possible. Still images after photographing are sequentially updated and displayed on the display device of the electronic camera every sequential shooting. It is, therefore, very difficult to perform sequential shooting while following an object by only the display device. In the following description, normal photographing will be called single shooting (photographing) with respect to sequential shooting (photographing).